Chirped pulse amplification is a technique for making energetic femtosecond laser pulses. In this technique, the peak power is reduced by stretching the pulse, then the pulse is amplified, and finally the original pulse width is restored through compression. Stretching/compression ratios may be as high as 5000, stretching a 50 femtosecond pulse to more than 2 nanoseconds for amplification. One difficulty in chirped pulse amplification techniques is the size of pulse stretchers and compressors.
Ultrashort Pulse Lasers (USPL), which can generate pico-second and femto-second laser pulses, require pulse stretchers and compressors. The stretchers and compressors currently known in the art are difficult to build and even more difficult to align. They are very sensitive to vibrations and minute perturbations. Also, they are generally custom-built and there are no suitable commercial off-the-shelf (COTS) alternatives.
Amplification for short pulse lasers operating in the near and mid wave infra-red (i.e. lasers with wavelengths of approximately 1 to 8 microns) is typically accomplished using difference frequency generation in an Optical Parametric Amplifier (OPA). This causes the OPA to generate an output pulse and an idler pulse according to the Manley-Rowe equation, which states that the inverse of the pump laser wavelength used to pump the OPA is equal to the sum of the inverses of the signal and idler output pulse wavelengths (1/λpump=1/λsignal1/λidler).
Recompressing the output pulse has been done in the past but with large and complex pulse stretchers and compressors. Typical pulse stretchers and compressors are large and have many sensitive components. A typical pulse stretcher volume is related to the amount of stretch. A small one could occupy approximately 5 ft3. The alignment tolerances in a typical pulse stretcher are very small, similar to interferometer tolerances. The critical lengths are generally in sub millimeters. This combination of large overall size and very tight alignment and critical length tolerances prevent a laser including such a typical pulse stretcher from tolerating vibrations, contamination, and temperature excursions. This type of laser (Chirped Pulse amplification or CPA) is has little to no chance of being mounted to a moving vehicle.
Typical pulse compressors share these size and alignment tolerance limitations of typical pulse stretchers. In typical high-power (joule per pulse) chirped-pulse amplification (CPA) laser systems, stretcher and compressor components typically take up a large portion of the system size. A CPA laser equipped with a typical pulse stretcher and a typical pulse compressor may have a total volume in excess of fifteen cubic feet, with the bulk of that occupied by the pulse stretcher and compressor. CPA systems having more than one stretcher or compressor may be even larger. Furthermore, because of the above-noted sub-millimeter alignment tolerances, such CPA systems are difficult to properly align and do not remain aligned outside of lab environments, making them unsuitable for practical applications and effectively unusable in any sort of field or mobile setting.